Periodic Reporting for period 4 - RHIZOCARBON (Forest belowground carbon transport: From rhizosphere fluxes to physiological drivers)
Reporting period: 2024-03-01 to 2024-08-31
Context
To facilitate predictions of carbon storage in changing climates and forests, scientists are looking at the trees. Tree carbon allocation dynamics are important, not only for tree eco-physiology, but also for global biogeochemistry. Despite extensive research in tree aboveground carbon fluxes, little is known about what is happening belowground.
Objective
The EU-funded RHIZOCARBON project investigated belowground carbon flow. It studied carbon flow in and between tree roots, including their fungal partners in the forest soil. Computational models were applied to identify the evolutionary requirements for the development of belowground carbon transfer. To trace belowground carbon transport, the project applied a new methodology of continuous in vivo combined measurement of 13CO2 carbon allocation and flux rate.
Conclusions
In terms of revealing the carbon balance of trees, we characterized tree carbon allocation dynamics in angiosperm and gymnosperm tree species, from photosynthesis to root exudation (Rog et al 2021). Next, we showed at high temporal and spatial resolution the tree carbon allocation in a mixed forest along two years (Rog et al 2024). In terms of deciphering mycorrhizal-induced carbon transfer among trees, we demonstrated mycorrhizal carbon sharing in a temperate forest (Rog et al 2020). Then we showed the patterns of belowground carbon transfer in a tree community (Avital et al 2022). Next, we identified the fungal species involved in pine-oak mycorrhizal carbon transfer (Cahanovitc et al 2022). In a complementary study, we detected the dynamics and chemistry of C transfer from pines to mushrooms (Rapaport et al 2024). Finally, we summarized the findings in the former papers to show that mycorrhizal networks exist (Klein et al 2023).
I would consider the above achievements as breakthroughs, because (1) a holistic tree carbon allocation scheme was so far missing; and (2) in the past three years there is a big debate about the role of mycorrhizal networks, and we were able to give compelling scientific evidence supporting their existence.
To facilitate predictions of carbon storage in changing climates and forests, scientists are looking at the trees. Tree carbon allocation dynamics are important, not only for tree eco-physiology, but also for global biogeochemistry. Despite extensive research in tree aboveground carbon fluxes, little is known about what is happening belowground.
Objective
The EU-funded RHIZOCARBON project investigated belowground carbon flow. It studied carbon flow in and between tree roots, including their fungal partners in the forest soil. Computational models were applied to identify the evolutionary requirements for the development of belowground carbon transfer. To trace belowground carbon transport, the project applied a new methodology of continuous in vivo combined measurement of 13CO2 carbon allocation and flux rate.
Conclusions
In terms of revealing the carbon balance of trees, we characterized tree carbon allocation dynamics in angiosperm and gymnosperm tree species, from photosynthesis to root exudation (Rog et al 2021). Next, we showed at high temporal and spatial resolution the tree carbon allocation in a mixed forest along two years (Rog et al 2024). In terms of deciphering mycorrhizal-induced carbon transfer among trees, we demonstrated mycorrhizal carbon sharing in a temperate forest (Rog et al 2020). Then we showed the patterns of belowground carbon transfer in a tree community (Avital et al 2022). Next, we identified the fungal species involved in pine-oak mycorrhizal carbon transfer (Cahanovitc et al 2022). In a complementary study, we detected the dynamics and chemistry of C transfer from pines to mushrooms (Rapaport et al 2024). Finally, we summarized the findings in the former papers to show that mycorrhizal networks exist (Klein et al 2023).
I would consider the above achievements as breakthroughs, because (1) a holistic tree carbon allocation scheme was so far missing; and (2) in the past three years there is a big debate about the role of mycorrhizal networks, and we were able to give compelling scientific evidence supporting their existence.
Overview of the results
In terms of revealing the carbon balance of trees, we characterized tree carbon allocation dynamics in angiosperm and gymnosperm tree species, from photosynthesis to root exudation (Rog et al 2021). Across the five species, C moved from leaves to stem and fine roots following an exponential decay, with parameters
that are consistent with the ecological role of each species. Next, we showed at high temporal and spatial resolution the tree carbon allocation in a mixed forest along two years (Rog et al 2024). Our study period included a drought year followed by an above-average wet year, offering an opportunity to test the effect of water availability on tree C allocation. We found that in comparison to the wet year, C uptake was lower in the dry year, C use was the same, and allocation to belowground sinks was higher. Among the five major C sinks, respiration was the largest (ca. 60%), while root exudation (ca. 10%) and reproduction (ca. 2%) were those that increased the most in the dry year. Most trees relied on stored starch for maintaining a stable soluble sugars balance, but no significant differences were detected in aboveground storage between dry and wet years. The detailed tree-level analysis of nonstructural carbohydrates and δ13C dynamics suggest interspecific differences in C allocation among fluxes and tissues, specifically in response to the varying water availability. Overall, our findings shed light on mixed forest physiological responses to drought, an increasing phenomenon under the ongoing climate change.
In terms of deciphering mycorrhizal-induced carbon transfer among trees, we demonstrated mycorrhizal carbon sharing in a temperate forest (Rog et al 2020). Then we showed the patterns of belowground carbon transfer in a tree community (Avital et al 2022). We found that carbon transfer was asymmetric, with oak being a better donor, and pistacia and cypress better recipients. Shared mycorrhizal species may have facilitated carbon transfer, but their diversity did not affect the amount, nor timing, of the transfer. Overall, our findings in a microcosm system expose rich, but hidden, belowground interactions in a diverse population of trees and mycorrhizal fungi. The asymmetric carbon exchange among cohabiting tree species could potentially contribute to forest resilience in an uncertain future. Next, we identified the fungal species involved in pine-oak mycorrhizal carbon transfer (Cahanovitc et al 2022). We demonstrate at a high temporal, quantitative, and taxonomic resolution, that carbon from ecto-mycorrhizal host trees moved into ecto-mycorrhizal fungi and that C was transferred further to neighboring trees of similar and distinct phylogenies. In a complementary study, we detected the dynamics and chemistry of C transfer from pines to mushrooms (Rapaport et al 2024). Carbon was assimilated in the labelled trees' needles and transferred to their roots. Starting from Day 2 after labelling, the C was transferred to adjacent sporocarps, peaking on Day 5. We identified more than 100 different labelled metabolites of different chemical groups present in roots and sporocarps. Of them, 17 were common to pine roots and both EMF species, and additional eight common to roots and one of the two EMF. The major labelled metabolites in the root tips were amino acids and tricarboxylic acid intermediates. The major labelled metabolites in sporocarps were amino acids, nucleotides, and fatty acids. We also identified labelled carbohydrates in all tissues. Labelling patterns diverged across different tissues, which can hint at how the C was transferred. Finally, we summarized the findings in the former papers to show that mycorrhizal networks exist (Klein et al 2023).
Exploitation and dissemination
We communicated our results to the Forest Service and discussed implications to forest management, to better account for belowground processes.
Our ERC project findings were shared on multiple media outlets. Two TV productions should be noted in particular:
NHK Japan: Nature’s Hidden Miracles Episode1 The Secret Life of Plants
ARTE Germany-France: Genius plants
In addition, some of our results were cited in an interview which was part of the 2022 NYT article "Are trees talking underground? For scientists, it's in dispute".
In terms of revealing the carbon balance of trees, we characterized tree carbon allocation dynamics in angiosperm and gymnosperm tree species, from photosynthesis to root exudation (Rog et al 2021). Across the five species, C moved from leaves to stem and fine roots following an exponential decay, with parameters
that are consistent with the ecological role of each species. Next, we showed at high temporal and spatial resolution the tree carbon allocation in a mixed forest along two years (Rog et al 2024). Our study period included a drought year followed by an above-average wet year, offering an opportunity to test the effect of water availability on tree C allocation. We found that in comparison to the wet year, C uptake was lower in the dry year, C use was the same, and allocation to belowground sinks was higher. Among the five major C sinks, respiration was the largest (ca. 60%), while root exudation (ca. 10%) and reproduction (ca. 2%) were those that increased the most in the dry year. Most trees relied on stored starch for maintaining a stable soluble sugars balance, but no significant differences were detected in aboveground storage between dry and wet years. The detailed tree-level analysis of nonstructural carbohydrates and δ13C dynamics suggest interspecific differences in C allocation among fluxes and tissues, specifically in response to the varying water availability. Overall, our findings shed light on mixed forest physiological responses to drought, an increasing phenomenon under the ongoing climate change.
In terms of deciphering mycorrhizal-induced carbon transfer among trees, we demonstrated mycorrhizal carbon sharing in a temperate forest (Rog et al 2020). Then we showed the patterns of belowground carbon transfer in a tree community (Avital et al 2022). We found that carbon transfer was asymmetric, with oak being a better donor, and pistacia and cypress better recipients. Shared mycorrhizal species may have facilitated carbon transfer, but their diversity did not affect the amount, nor timing, of the transfer. Overall, our findings in a microcosm system expose rich, but hidden, belowground interactions in a diverse population of trees and mycorrhizal fungi. The asymmetric carbon exchange among cohabiting tree species could potentially contribute to forest resilience in an uncertain future. Next, we identified the fungal species involved in pine-oak mycorrhizal carbon transfer (Cahanovitc et al 2022). We demonstrate at a high temporal, quantitative, and taxonomic resolution, that carbon from ecto-mycorrhizal host trees moved into ecto-mycorrhizal fungi and that C was transferred further to neighboring trees of similar and distinct phylogenies. In a complementary study, we detected the dynamics and chemistry of C transfer from pines to mushrooms (Rapaport et al 2024). Carbon was assimilated in the labelled trees' needles and transferred to their roots. Starting from Day 2 after labelling, the C was transferred to adjacent sporocarps, peaking on Day 5. We identified more than 100 different labelled metabolites of different chemical groups present in roots and sporocarps. Of them, 17 were common to pine roots and both EMF species, and additional eight common to roots and one of the two EMF. The major labelled metabolites in the root tips were amino acids and tricarboxylic acid intermediates. The major labelled metabolites in sporocarps were amino acids, nucleotides, and fatty acids. We also identified labelled carbohydrates in all tissues. Labelling patterns diverged across different tissues, which can hint at how the C was transferred. Finally, we summarized the findings in the former papers to show that mycorrhizal networks exist (Klein et al 2023).
Exploitation and dissemination
We communicated our results to the Forest Service and discussed implications to forest management, to better account for belowground processes.
Our ERC project findings were shared on multiple media outlets. Two TV productions should be noted in particular:
NHK Japan: Nature’s Hidden Miracles Episode1 The Secret Life of Plants
ARTE Germany-France: Genius plants
In addition, some of our results were cited in an interview which was part of the 2022 NYT article "Are trees talking underground? For scientists, it's in dispute".
As detailed above, our progress had both novel methodologies and inter-disciplinary developments. As far as we can tell, our research was the first to use the DNA-SIP methodology for mycorrhizal detection. In addition, our collaboration with the research team of Prof. Lilach Hadany (Tel Aviv University) demonstrates a new and inter-disciplinary development in the study of mycorrhizal network formation.
The vast majority of the project's results has been published in the papers cited above. Remaining results are those pertaining to the ecological significance of mycorrhizal-induced carbon transfer among trees. We monitored the carbon flow from a 13CO2-labelled donor pine tree to a below-ground connected oak tree and demonstrated C transfer from pines to shaded oaks. We also identified the main fungal symbionts interacting with pines and oaks.
The vast majority of the project's results has been published in the papers cited above. Remaining results are those pertaining to the ecological significance of mycorrhizal-induced carbon transfer among trees. We monitored the carbon flow from a 13CO2-labelled donor pine tree to a below-ground connected oak tree and demonstrated C transfer from pines to shaded oaks. We also identified the main fungal symbionts interacting with pines and oaks.